i think lwp does the right thing, but TestRequest.pm does not. patch below should fix (untested).
--- Apache-Test/lib/Apache/TestRequest.pm 4 Apr 2002 00:54:26 -0000 1.71 +++ Apache-Test/lib/Apache/TestRequest.pm 17 Sep 2002 20:22:38 -0000 @@ -251,7 +251,7 @@ $credentials{$keep->{realm} || '__ALL__'} = [$keep->{username}, $keep->{password}]; } - if (my $content = $keep->{content}) { + if (defined(my $content = $keep->{content})) { if ($content eq '-') { $content = join '', <STDIN>; }